Polyadenylated RNA and RNA-Binding Proteins Exhibit Unique Response to Hyperosmotic Stress.

Benjamin L Zaepfel,Jeffrey D Rothstein

doi:10.3389/fcell.2021.809859

Benjamin L Zaepfel, Jeffrey D Rothstein

Open Access

https://doi.org/10.3389/fcell.2021.809859

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Abstract

Stress granule formation is a complex and rapidly evolving process that significantly disrupts cellular metabolism in response to a variety of cellular stressors. Recently, it has become evident that different chemical stressors lead to the formation of compositionally distinct stress granules. However, it is unclear which proteins are required for the formation of stress granules under different conditions. In addition, the effect of various stressors on polyadenylated RNA metabolism remains enigmatic. Here, we demonstrate that G3BP1/2, which are common stress granule components, are not required for the formation of stress granules specifically during osmotic stress induced by sorbitol and related polyols. Furthermore, sorbitol-induced osmotic stress leads to significant depletion of nuclear polyadenylated RNA, a process that we demonstrate is dependent on active mRNA export, as well as cytoplasmic and subnuclear shifts in the presence of many nuclear RNA-binding proteins. We assessed the function of multiple shifted RBPs and found that hnRNP U, but not TDP-43 or hnRNP I, exhibit reduced function following this cytoplasmic shift. Finally, we observe that multiple stress pathways lead to a significant reduction in transcription, providing a possible explanation for our inability to observe loss of TDP-43 or hnRNP I function. Overall, we identify unique outcomes following osmotic stress that provide important insight into the regulation of RNA-binding protein localization and function.

Highlights

Nuclear RNA binding proteins (RBPs) perform a broad range of functions to process mRNA from transcription to nuclear export
G3BP1/2 are not Required for Stress Granule Formation During Hyperosmotic Stress
Both G3BP1 and G3BP2 have both been demonstrated as resident protein components of stress granules (SGs) that form in response to cellular stress (Matsuki et al, 2013)

Summary

Introduction

Nuclear RNA binding proteins (RBPs) perform a broad range of functions to process mRNA from transcription to nuclear export. The proper processing and maturation of mRNA depends on the temporal and spatial availability of the necessary RBPs. The improper regulation of RBPs and maturation of RNA contributes to the physiology of numerous diseases, including amyotrophic lateral sclerosis (Vanderweyde et al, 2017), fragile X mental retardation syndrome (Vanderweyde et al, 2017), and a variety of cancer subtypes (Qin et al, 2020). A recent comprehensive study identified numerous interactions between RBPs and their target RNAs (Van Nostrand et al, 2020). While this work provides significant insight into the localization and interactions of RBPs in an unperturbed cellular environment, it is important to understand how RBPs and RNA respond to stimulus such as cellular stress.

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